This invention relates to a torque detecting apparatus. More particularly, it relates to a torque detecting apparatus for numerically detecting the torque transmitted between a driving member and a driven member, that is, an amount of angular displacement produced between the two members when both are rotatingly linked with a transmitting means which is so disposed between the two members as to permit relative angular displacement. This invention also relates to an apparatus for detecting relative angular displacement between two rotary members.
In the apparatus of prior art U.S. Pat. No. 4,193,720, the torque between the two members is detected, as disclosed in the specification and drawings thereof, while the driving member and the driven member are rotated via a flexible driving connection. In this apparatus, the driving member is provided with a reaction rod which is integrally rotatable therewith and also axially movable. On one end of the reaction rod and on the corresponding end of the driven member cam surfaces are respectively disposed so as to be mutually engaged due to spring force applied on the reaction rod. When the driven member is placed under a load exceeding a predetermined amount, some angular displacement takes place between the driven member and the driving member, which will cause the reaction rod to be axially moved against the spring force due to the action between the cam surfaces. The torque between both members can be measured in this apparatus by detecting the amount of shift of the reaction rod.
As the reaction rod is axially shifted in this prior art apparatus through the action between the two cam surfaces formed on the driven member and the reaction rod, the detected value is liable to be varied according to the lubrication status of the cam surfaces, and moreover the detected value may possibly go wrong due to the easy axial shifting of the reaction rod caused by variation of the slant angle between the cam surfaces when they have been worn, which will inevitably vary the detected value.
Other prior art devices are known from TOKU-KO-SHO Nos. 53(1978)-22474 and 54(1979)-6101 published in Japan.
According to the disclosure in TOKU-KO-SHO No. 53(1978)-22474, the driving shaft and the driven shaft are each provided with a magnet, and proximity switches are disposed in the circumference thereof. A load torque applied to the driven shaft can be detected by measuring the phase difference of the pulse signals generated from both proximity switches, i.e., the magnitude of the relative angular displacement between both magnets which is proportional to the magnitude of the torque. As a base or reference for setting the predetermined load torque, i.e., the maximum allowable phase difference, a mono-stable multivibrator, which is able to keep for a certain time (maximum phase difference) an ON state in response to activation of the proximity switch on the driving shaft side, is used. In a time constant circuit determining the ON time for the multivibrator, setting of an exact time is quite difficult, and exact load torque detection is therefore next to impossible. Detection of a lesser load torque value which has been lowered from a certain level is difficult in this prior art. After all, simple and exact detection of the torque has not been established so far. It is also impossible in this prior art apparatus which makes use of the phase difference to detect the varying status and the value of the torque on the driven shaft while it is in rotation at each moment.
In the disclosures of TOKU-KO-SHO No. 54(1979)-6101 the value of load torque to be detected is set in advance. For detecting various predetermined load torques, the mounting condition of detected or detecting members must be altered case by case. Just like in the above-mentioned prior art device, detection of a small amount of torque and variation of the torque can not be made satisfactorily in this prior art apparatus.